ev, A. V. Nechaev, and N. M. Chasovskikh UDC 626.823.92 Tunnel spillways are widely used at hydro developments with dams on rock foundations being constructed at confined sites. Their use usually makes it possible to have a broad front of earthworks thanks to diversion of the stream through underground conduits and also to reduce the cost of construction in cases when the construction of an open outlet is related to considerable difficulties. The expediency of constructing such spillways is substantiated by technical and economic calculations. A variant of a shaft tunnel spillway was adopted when designing the hydro development of the Alindzhachai reservoir in the Nakhichevan ASSR.The following variants of outlet works were examined: traditional shaft spillway with a vertical circular shaft; spillway with an inclined shaft.However, as is known, all shaft spillways have a number of substantial shortcomings, the principal ones of which are the uncertainty of operation of the shaft and the danger of cavitation during passage of the flow.

This paper is devoted to the electrochemical and chemical aspects of the erosion-corrosion destruction of the surface layer of a wet-steam turbine rotor blade under the influence of an electrified working fluid. It considers a hypothesis about a complex mechanochemical-electrochemical mechanism of chromium and iron wash-out from the surface layer of the rotor blade metal during the destruction of the oxide film under the influence of a high-speed wet steam flow. Various versions of this process are analyzed for positive, negative, quasi-neutral, and neutral electrifications of wet steam. The possibility to hydrogenate the surfaces of rotor blades under the influence of negatively-charged droplets is shown theoretically. The damage to the blades in this case is similar to that from anodic etching. It is also shown that the process of blade surface hydrogenation takes place in any case both for electrically-charged droplets and for neutral ones. However, in the case of neutral droplets, the intensity of the process is insignificant. An experimental study was carried out for the erosion-damaged surface of a last-stage rotor blade from of the BK-50 LMP turbine that had exhausted its lifetime. The quantitative content of chromium was determined in the steel sample cut out from the blade. A decrease in chromium content in the erosion-damaged blade surface layer was found. To test the hypothesis about the similarity between the process of anodic electro-etching and the process of surface destruction under the influence of negatively-charged droplets, an electrochemical experiment was carried out on a model sample of 20X13 chromium steel. The reliefs of the damaged areas on the model sample after anodic etching and on the observable blade in the zone of exposure to negatively-charged droplets are shown to be similar. The experimental studies have confirmed the presence of a complex mechanochemical-electrochemical process of blade destruction. On the basis of the data obtained, recommendations for extending the useful life of turbine blades are formulated.

No abstract

It has been established that in order to study thermo- and electrophysical phenomena in wet steam turbines, studies of the wet steam flow volume charge effect on its dielectric and thermophysical properties have recently been carried out at A. Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine. According to their results, it was established that the most representative electrophysical parameter, which allows to evaluate changes in the thermophysical properties of steam, which occur under the action of its own volume charge, is its dielectric constant. It is assumed that the value of the dielectric constant of an electrified steam can be significantly different from the value for a neutral steam, and a mathematical assessment of its possible change is made. It has been confirmed that the influence of electrophysical phenomena caused by the wet steam flow electrification is significant, but is not taken into account in the existing physical and mathematical thermodynamic models of the steam expansion process. It is proved that in order to clarify the main thermodynamic parameters and calculated characteristics of the electrified wet steam flow, it is necessary to determine how its dielectric constant changes. On the basis of the analysis, the relevance of experimental determination of the dielectric constant of a wet steam flow with a volume charge in order to obtain the dependence of its change on the temperature and pressure of the flow, as well as the density of the volume charge, is substantiated. To perform the research, a gas dynamic laboratory plant, which allows to obtain a wet steam flow with a volume charge, was used. The internal space of the flow part of a real wet steam turbine has a significant size and allows the formation of a flow with a volume charge of a complex spatial configuration and structure. It is emphasized that in the flow part of the plant of a small volume, in contrast to the turbine flow part, significant technical difficulties arise when organizing the conditions for the occurrence of a wet steam flow with a volume charge. Taking this into account, at the first stage, it was decided to conduct a study of a steam flow with a volume charge flowing into the atmosphere in a laboratory room with a sufficient volume to form its spatial structure. To estimate the value of its dielectric constant, the inductive method (L-method) of determining dielectric properties, in which the substance under study is introduced into the inductive solenoid cell, was chosen. Experiments were conducted and, according to the obtained data, it is possible to make a preliminary assessment of the change in dielectric constant in the presence of a volume electric charge in the steam flow